The present invention relates to a system for monitoring movement in three mutually perpendicular directions in structures, and more particularly to a system for detecting movement in underground tunnels.
Underground tunnels such as are used for automobile and rail river crossings are generally quite long, and subject to substantial overburden loads. Typically the tunnels are designed to permit some degree of movement of the tunnel to accomodate variations in the overburden and other loads on the tunnel. The amount of tunnel movement normally permitted will be several inches over a substantial length of the tunnel, without causing any structural damage to the tunnel. However, tunnel movements must be monitored, or at least checked periodically, to determine whether excessive movements have occurred, or whether the rate of movement is increasing. These data on tunnel movements provide a basis for deciding whether remedial action is required. If construction near the tunnel is contemplated, or in progress, continual monitoring of tunnel movement is obviously preferred, as it can provide an early warning indication of a deteriorating situation, such as might occur where a landfill is built above or adjacent to a submerged tunnel at a river crossing or, when nearby construction might cause tunnel movement or deformation.